The invention relates to a directly heatable crucible for induction melting furnaces, particularly for melting refractory and highly-pure metals. An induction coil surrounds the crucible and a housing at least partially encloses the inductor coil and the crucible and forms a closed chamber together with the external wall of the crucible.
A process is known for melting refractory metals, particularly tantalum, tungsten, thorium or alloys of these metals in a water-cooled crucible (DE 518 499); the crucible is made of materials which have a lower melting point than the material to be molten, e.g. made of quartz glass, copper or silver. The energy required for the melting process as well as for the cooling of the crucible is supplied such that the material is completely molten without causing impurities by the crucible material.
Furthermore, a replaceable, pounded crucible is known for grooveless induction melting furnaces including a metallic, non-live, basket-like frame which surrounds the crucible or which is incorporated in the external wall thereof (CH 315 944). The frame is composed of water-cooled, flat or oval pipes made of a non-magnetic material.
Also known is an induction melting furnace including a replaceable crucible (U.S. Pat. No. 3,162,710) which has an insert made of refractory material and can be inserted into an external sleeve of sheet metal. This external sleeve is surrounded by an inductor coil which, at the same time, serves as a cooling element. The inductor coil, in turn, is supported by a rack which is configured as a hollow cylinder.
Further, a device for melting and casting titanium has been suggested (U.S. Pat. No. 3,383,840) wherein the crucible is a sleeve made of graphite which is surrounded by a pot-like jacket made of a relatively thin-walled ceramic material. The inductor coil which, in turn, encloses the graphite jacket is surrounded by a hood which rests on a base plate as does the crucible.
Finally, a device is known for melting reactive metals and metal alloys (EP 0 276 544), to which U.S. Pat. No. 4,738,713 corresponds wherein the crucible is made of stave-like metal rods which are provided with vertically running pocket holes in which end thin-walled pipes. These pipes are used to feed cooling water into the pocket holes. The metal rods which form narrow, vertically extending gaps between two adjacent rods are connected to one another as one piece via the base plate under which the feed lines are disposed for supplying the cooling agent to the thin-walled pipes.
These known induction melting furnaces have the particular disadvantage that a large portion of the electric energy which is necessary for the melting process is already lost in the crucible.